/**
*      author: Y_Yao
*      created: 2024-12-21 20:15:23
**/

#include<bits/stdc++.h>

#define int LL
using namespace std;
using LL = long long;
const LL LLINF = 1e18;
const int INF = 0x3f3f3f3f;
const int N = 3000 + 7;
int a[N];
int dp[N][N];
int n;

void solve()
{
    cin >> n;
    for(int i = 1;i <= n;i++)
    {
        cin >> a[i];
    }

    memset(dp,1,sizeof(dp));
    for(int i = 1;i <= n;i++)
    {
        for(int j = 1;j <= n;j++)
        {
            dp[i][j] = 1;
        }
    }
    // for(int i = 1;i <= n;i++)
    // {
    //     for(int j = 1;j <= n;j++)
    //     {
    //         cout << dp[i][j] << " ";
    //     }
    //     cout << endl;
    // }
    int ans = 0;
    for(int i = 1;i <= n;i++)
    {
        for(int j = 1;j <= i;j++)
        {
            if(a[i-j] == a[i])
            {
                dp[i][j] = dp[i-j][j] + 1;
            }
            ans = max(ans,dp[i][j]);
        }
    }
    cout << ans << endl;
}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}

